The combined cycle power generation has been commercially practiced in which a gas turbine is driven by a gas of high temperature and high pressure that is generated by burning a fuel such as natural gas, while steam generated by using waste heat from the gas turbine is used to drive a steam turbine.
While natural gas is predominantly used as the fuel for these gas turbines, use of natural gas involves problems such as the high cost of storing and transporting the natural gas.
To avoid these problems, technologies have recently been developed to manufacture refined oil, which can be used as the gas turbine fuel oil, instead of the natural gas, from crude oil.
Japanese Patent Publication, First Publication No. 6-209600 discloses a technology to prepare refined oil which is preferably used as the gas turbine fuel oil by having low-sulfur crude oil react with hydrogen in the presence of a desulfurizing catalyst, thereby reducing the content of sulfur and heavy metals in the refined oil.
However, since the method disclosed in the publication mentioned above requires the use of low-sulfur crude oil as the raw material, a large amount of sulfur is included in the refined oil in the case of crude oil which has a high sulfur content is used. This results in the exhaust gas from the gas turbine containing a large amount of sulfur oxide, which is a problem that must be solved for environmental conservation.
Japanese Patent Publication, First Publication No. 2000-273467 (first publication date: Oct. 3, 2000) discloses a technique for producing a gas turbine fuel oil by hydrogenation of gas oil which has been obtained from crude oil through processes such as fractional distillation and solvent deasphalting, in the presence of a demetalizing/desulfurizing catalyst.
This method of refining gas oil by hydrogenation is capable of yielding refined oil suitable as a fuel having a viscosity of 4 cst or less, an alkali metal content of 1 wt ppm or less, a lead content of 1 wt ppm or less, a vanadium content of 0.5 wt ppm or less, a calcium content of 2 wt ppm or less, and a sulfur content of 500 wt ppm or less.
However, this method of manufacturing refined oil has problems such as the following.
(1) When heavy species of oil (heavy oil which includes a large amount of high-boiling point components and high concentration of ashphaltene such as, for example, crude oil, atmospheric residue, vacuum residue, deasphalted oil made from these species of oil through solvent deasphalting, vacuum gas oil and tar sand) are used as the feed oil, the viscosity of the refined oil prepared may be higher than the value described above. Use of such refined oil as the fuel results in problems such as poor atomizing characteristics of the fuel oil and poor combustion characteristics in the gas turbine.
(2) Although it is possible, even when a heavy species of oil is used as the feed oil, to lower the viscosity and pour point of the gas oil which is charged to hydrogenation refining process by regulating the operating conditions of the fractional distillation process and solvent deasphalting process while decreasing the yield of the refined oil, this leads to higher production cost due to the lower yield of the refined oil.
(3) Also, when heavy species of oil are used as the feed oil for the purpose of preparing refined oil for broad applications such as petrochemical industrial material, too it is possible to lower the viscosity and pour point of the refined oil by increasing the reaction temperature and pressure of the hydrogenation refining process. However, the effects tend to be insufficient, and in addition, increases in the operation cost and equipment cost cannot be avoided.